In normal vision, the two human eyes perceive views of the world from different perspectives due to their separate location within the head. These two perspectives are then used by the brain to assess the distance to various objects in a scene. In order to build a display which will effectively display a three dimensional image, it is necessary to re-create this situation and supply a so-called “stereoscopic pair” of images, one to each eye of the observer.
Three-dimensional displays are classified into two types depending on the method used to supply the different views to the eyes. Stereoscopic displays typically display both of the images over a wide viewing area. However, each of the views is encoded, for instance by colour, polarisation state or time of display, so that a filter system of glasses worn by the observer can separate the views and will only let each eye see the view that is intended for it.
Autostereoscopic displays require no viewing aids to be worn by the observer but the two views are only visible from defined regions of space. The region of space in which an image is visible across the whole of the display active area is termed a “viewing region”. If the observer is situated such that one of their eyes is in one viewing region and the other eye is in the viewing region for the other image of the pair, then a correct set of views will be seen and a three-dimensional image will be perceived.
For flat panel autostereoscopic displays, the formation of the viewing regions is typically due to a combination of the pixel structure of the display unit and an optical element, generically termed a parallax optic. An example of such an optic is a parallax barrier. This element is a screen with vertical transmissive slits separated by opaque regions. This screen can be set in front of a spatial light modulator (SLM) with a two-dimensional array of pixel apertures as shown in FIG. 1.
The display comprises a transmissive spatial light modulator in the form of a liquid crystal device (LCD) comprising an active matrix thin film transistor (TFT) substrate 1, a counter substrate 2, a pixel (picture element) plane 3 formed by a liquid crystal layer, polarisers 4 and viewing angle enhancement films 5. The SLM is illuminated by a backlight (not shown) with illumination in the direction indicated by an arrow 6. The display is of the front parallax barrier type and comprises a parallax barrier having a substrate 7, an aperture array 8 and an anti-reflection (AR) coating 9.
The SLM is arranged such that columns of pixels are provided extending vertically for normal viewing with the columns having a horizontal pitch p. The parallax barrier provides an array 8 of apertures or slits with the slits being parallel to each other and extending parallel to the pixel columns. The slits have a width 2w and a horizontal pitch b and are spaced from the pixel plane 3 by a separation s.
The display has an intended viewing distance ro with left and right viewing windows 10 and 11 at the widest parts of the viewing regions defining a window plane 12. The viewing windows 10 and 11 have a pitch e which is generally made substantially equal to the typical or average human eye separation. The centre of each primary viewing window 10, 11 subtends a half angle a to the display normal.
The pitch b of the slits in the parallax barrier is chosen to be close to an integer multiple of the pixel pitch p of the SLM so that groups of columns of pixels are associated with a specific slit of the parallax barrier. FIG. 1 shows an SLM in which two pixel columns are associated with each slit of the parallax barrier.
The windows 10 and 11 are formed by the cooperation of each slit of the parallax barrier 7-9 with the pixels associated with it. However, adjacent pixels may cooperate with each slit to form additional viewing windows (not shown) which are located on either side of the windows 10 and 11 in the windows plane 12. The windows 10 and 11 are referred to as primary viewing windows whereas any additional windows are referred to as secondary viewing windows.
FIG. 2 of the accompanying drawings shows the angular zones of light created from an SLM and parallax barrier where the parallax barrier has a pitch b of an exact integer multiple of the pixel column pitch p. In this case, the angular zones coming from different locations across the display panel surface intermix and a pure zone of view for image 1 or image 2 does not exist. In order to address this, the pitch b of the parallax optic is reduced slightly so that the angular zones converge at the window plane 12 in front of the display. This change in the parallax optic pitch is termed “viewpoint correction” and is shown in FIG. 3 of the accompanying drawings. The viewing regions created in this way are roughly kite shaped.
For a colour display, each pixel is generally provided with a filter associated with one of the three primary colours. By controlling groups of three pixels each with a different colour filter, substantially all visible colours may be produced. In an autostereoscopic display, each of the stereoscopic image “channels” must contain sufficient of the colour filters for a balanced colour output.
Another known type of directional display is the rear parallax barrier display as shown in FIG. 4 of the accompanying drawings. In this case, the parallax barrier 7, 8 is placed behind the SLM 1 to 5 i.e. between the SLM and the backlight. This arrangement has the advantage that the barrier is kept behind the SLM away from possible damage.
Lenticular screens are used to direct interlaced images to multiple directions, which can be designed to give a 3D image or give multiple images in multiple directions. Practical lenses tend to suffer from scatter and poor anti-reflection performance so that the surface is very visible in both ambient and backlit environments. Therefore, the image quality of lenticular screens can be poor and the system suffers from similar problems as parallax barriers such as the need for close proximity to the image pixels. An array of prism structures may be used in a similar way.
Holographic methods of image splitting also exist but they suffer from viewing angle problems, pseudoscopic zones and a lack of easy control of the images.
Micropolariser displays use a polarised directional light source and patterned high precision micropolariser elements aligned with the LCD pixels. Such a display offers the potential for high window image quality as well as 2D/3D function in a compact package. The dominant requirement is the incorporation into the LCD of micropolariser elements to avoid parallax issues.
FIG. 5 illustrates three known types of dual view displays referred to as P1, P2 and P3. Each of these displays is of the front parallax barrier type but could equally well be of the rear parallax barrier type or could be embodied using different types of parallax optics. The P1 display comprises an LCD 20a comprising columns of pixels displaying the two views as interlaced vertical strips with left and right strips being displayed by interlaced single columns of pixels. FIG. 5 illustrates the displays as being autostereoscopic 3D displays with a viewer being illustrated at 30. A column 21a of pixels displays a strip of the right eye image whereas a column 22a displays a strip of the left eye image. The adjacent columns 23a and 24a display left eye and right image strips, and so on across the LCD 20a. A parallax barrier 25a is disposed in front of the LCD 20a and controls which pixel columns are visible to which eye of the viewer 30 in the usual way.
The P2 display differs from the P1 display in that pairs of adjacent pixel columns display a strip of one of the views. For example, the pair of adjacent pixel columns 21b and 23b and the pair of adjacent pixel columns 26b and 27b display respective strips of the right eye view whereas the pair of pixel columns 22b and 24b and the pair of pixel columns 28b and 29b display respective strips of the left eye view. The barrier 25b provides wider slits of larger pitch spaced further from the LCD 20b than the barrier 25a for the P1 display. Thus, each eye of the observer 30 can see two columns of pixels through each slit of the barrier 25b. 
The P3 display differs from the P1 and P2 displays in that each eye of the viewer 30 sees three columns of pixels through each slit of the parallax barrier 25c and each strip of each of the two views displayed by the LCD 20c is displayed by three adjacent columns of pixels. Thus, the pixel columns 21c, 23c, 28c and the pixel columns 27c, 31c, 32c display two strips of the left eye view whereas the pixel columns 22c, 24c, 26c and the pixel columns 29c, 33c, 34c display two strips of the right eye view.
In general, displays can be classified as being of Pn type where, in each primary viewing window, n columns of pixels are viewable and each strip of each view is displayed by n adjacent columns of pixels. Pn displays where n is greater than one have advantages over P1 displays in that higher resolution LCD panels or larger separation between the barrier slit plane and the pixel plane can be used without changing the viewing distance of display at which viewpoint correction is provided, i.e. the window plane. However, such displays have disadvantages in that the barrier structure may be more visible to the viewer and colour defects as described hereinafter may be produced.
FIG. 6 illustrates a P2 type of display in which a conventional vertically striped colour filter (or vertical strips of colour pixels) is used. Thus, the colour filter comprises a repeating pattern of vertical red (R), green (G), and blue (B) strips (or intrinsically coloured pixels are arranged in this way). The effect of this for one view is illustrated at 35. In particular, the order of colours seen in that view is not the RGBRGB . . . pattern of the underlying colour pixels but, instead, is RGGBBRRG . . . .
Thus, the viewer may perceive red, green and blue strips on a scale which is four times larger than the pitch of the pixel columns.
FIG. 7 illustrates a P3 type of display, again having pixel colours arranged as repeating RGB columns. When viewed from the middle of a viewing window, there are no undesirable colour artifacts and the red, green and blue pixel colours are visible in the correct ratios through each slit of the barrier 25.
FIG. 8 illustrates what happens when adjacent groups of pixels for left and right images display different image data. In particular, by way of example, each set of three pixel columns such as 36 for the left eye image is shown displaying white whereas the pixel columns such as 37 displaying the right eye image are shown as being black. When the display is viewed from the centre of each viewing window as illustrated at 38, there are no undesirable visual artifacts.
FIG. 8 illustrates at 39 the effect of a viewer moving to the left as compared with the situation illustrated at 38. This is equivalent to a relative movement to the right of the barrier 25. The effect of this is that each red column of pixels of the left eye view becomes increasingly obscured. Although the red pixels of the right eye view become visible, because they are black, the effect is that there is a colour shift towards cyan in the left eye view as perceived by the viewer. Thus, colour artifacts which are dependent on the image being displayed are perceived by the viewer when viewing the display from other than the optimal position.
GB2399653 discloses a non-periodic parallax barrier structure in which groups of evenly spaced slits are themselves evenly spaced apart with a different horizontal pitch. Vertically striped colour filtering is also disclosed.
WO02091348 discloses a single view or two-dimensional (2D) display having a non-standard pattern of pixel colouring.
DE19822342 discloses a multiple view display of the P3 type. In order to allow for lateral movement of an observer without shifting a parallax barrier structure relative to a pixel structure, columns of pixels additional to those viewable through each slit when the display is viewed correctly are switched.
Schmidt et at, “Multi-Viewpoint Autostereoscopic Displays from 4D-Vision”, Proc. SPIE, vol. 4660, pp 212-221 (2002) and Son et at, “Moiré Pattern Reduction in Full-Parallax Autostereoscopic Imaging Systems Using Two Crossed Lenticular Plates as a Viewing Zone Forming Optics”, Proceedings of the tenth International Display Work-shop-Fukuoka 2003, paper 3D2-2 disclose so-called staggered parallax barriers in which the slits are arranged at an acute angle to the column direction of the display structure. Such arrangements are disclosed for reducing Moiré patterning in displays of the P1 type.
EP 1 427 223 and EP 0 829 743 discloses P1 displays with repeating groups of RGB columns.
EP 1 401 216, EPO 0 860 728, US 2002/0001128 and EP 0 847 208 discloses viewer position indications in P1 displays.